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    <script>
        // ES6中，允许为函数的参数设置默认值

        // function abc(x = 2, y = 4) {
        //     console.log(x + y);
        // }
        // abc();
        // abc(6);
        // abc(6, 6);

        function aaa(x=5,y){
            console.log(x + y);
        }
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